Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $89.91   3.799%   $93.3257   $93.33   $93.35   $93.30  
  Purchase #2 $168.46   8.533%   $182.8347   $182.83   $182.85   $182.80  
  Purchase #3 $103.52   12.341%   $116.2954   $116.30   $116.30   $116.30  
  Purchase #4 $57.26   8.292%   $62.008   $62.01   $62.00   $62.00  
  Purchase #5 $23.44   7.675%   $25.239   $25.24   $25.25   $25.20  
  Purchase #6 $114.82   9.480%   $125.7049   $125.70   $125.70   $125.70  
  Purchase #7 $147.71   8.724%   $160.5962   $160.60   $160.60   $160.60  
  7 purchase totals = $705.12       $766.0039   $766.01   $766.05   $765.90